Satellite and other wireless communication platforms often employ a large number of narrow spot beams that form a cellular coverage of a wide geographic area. It is preferred that the alignment of the spot beams is maintained so that complete coverage of the geographic area is maintained. The spot beam patterns are nominally fixed unless the platform is perturbed, or as the antenna characteristics change. The device itself may be perturbed by various forces including the gravitational effects of various heavenly bodies. The antenna's characteristics may change in response to factors such as sun-induced warping. Spot beam pattern changes may be simulated by computer but cannot be easily measured in an operational system.
Satellites systems typically employ star trackers to help maintain the alignment of the satellite. However, even if the satellite is accurately maintained, the antenna may still contribute to pointing errors. Star trackers are expensive and add mass to the satellite. One goal of satellite implementations is to reduce the mass of the satellite. Thus, it would be desirable to eliminate such components as a star tracker.
Communication systems sometimes use closed-loop beacon tracking systems. Such systems use a transmitter on the ground and one or more receiving beams on the satellite. A closed-loop system operates to null a signal. When the tracking signal is nulled, the antenna is correctly pointed at the beacon location. Even though the antenna is pointed correctly, the antenna pattern may still be incorrect. Beacon tracking systems also add hardware and mass to the communication platform.
It would therefore be desirable to eliminate star trackers or beacon tracking systems in a communication platform while allowing the communication platform to be accurately positioned and adjusted relative to the beam pattern.